1. Field Of The Invention
The present invention relates generally to blast cleaning systems used for cleaning surfaces by the abrasive action of sand or other abrasive media borne by a carrier fluid which is typically compressed air, forced against the surface to be cleaned under high pressure. In a more specific sense, the invention relates to blast-cleaning devices designed to clean the interior surfaces of pipes. These are often mounted on traveling carriages that are moved through the pipes to be cleaned, and which have blast nozzles rotating at high speed in reaction to the force of the carrier fluid supplied to the nozzles as the device moves along the length of the pipe.
2. Description Of The Prior Art
Heretofore, it has been well known to provide traveling carriages, that move through the length of a pipe or other tubular object that is to be cleaned, with said carriages being adapted to support high speed, rotating nozzles through which compressed air is directed, against the surface of the pipe. In devices of this type, abrasive media are carried by the air, sand being a typical medium used for the purpose of cleaning the internal surface of the pipe.
In devices of this type, the nozzle rotates reactively to the force of the compressed air directed therethrough. It is common, further, for the compressed air to be supplied to the traveling device, through a hose, to a non-rotatable conduit.
In devices of this type, as a result, problems arise resulting from the fact that it is necessary to supply the compressed air under high pressure first through a non-rotating conduit, and then to a freely rotatable nozzle support shaft mounted in the housing supported on the traveling carriage. The basic problem in apparatus of this type is that a sealing gasket must be employed between the rotating and non-rotating components, and this gasket obviously becomes subject to heavy wear, by reason of the fact that the compressed air is supplied under high pressure, and further by reason of the fact that the compressed air carries abrasive media which is forced against the gasket, tending to cause deterioration of the gasket with undesirable rapidity.
Usually, a leather seal or gasket is employed between the rotating and non-rotating members. It has been found, in the art to which the invention is directed that maintaining exactly the right pressure on the seal is a highly critical requirement. If excessive pressure is used, the rotating member is prevented from spinning with the freedom requisite to proper operation of the cleaning system.
Conversely, if too little pressure is exerted upon the seal, an excessive amount of abrasive and air leaks through the joint between the rotating and non-rotating members. It has been proposed, in this regard, that once the tightness of the rotating joint is judged to be correct, after threadedly advancing the non-rotating conduit against the seal to compress it to the desired extent, one can lock the conduit in the position to which it is threadedly advanced, and in this way preserve the adjustment. The problem, however, is that during regular operation the rotation of the nozzle support shaft causes rapid wear of the seal, requiring frequent re-adjustments.
Commonly, the rotation seal, and the bearings and bearing seals of the nozzle support shafts, are all enclosed in a common housing. The known tendency of leakage of abrasive past the seals results in penetration of the bearings and bearing seals by the abrasive, with obviously destructive effect thereon. It is common, indeed, to remove and clean the bearings at the end of every work shift.
It has been proposed to provide an air gap to permit dispersal of the leaking abrasive to the ambient atmosphere, so as to prevent it from penetrating the bearings and bearing seals of the nozzle support shaft. However, so far as is known, a completely satisfactory result has not been obtained in devices heretofore making use of this concept, by reason of the fact that the only way in which pressure on the sealing gasket has been adjusted, when a gap open to ambient atmosphere is used, is by adjusting the width of the gap through the use of shims that must be added or removed according to the needs of the particular situation. This is an undesirably cumbersome procedure, and even when employed, does not necessarily assure the precise, fine adjustments of pressure that should desirably be embodied in a spin blast apparatus of the type described previously herein.